Hexafluoroisobutylene is a known compound which is known to be useful for a variety of purposes such as, for example, a comonomer which forms polymers of exceptional thermal, chemical and mechanical properties with other comonomers such as vinylidene fluoride. The preparation of such copolymers is described in U.S. Pat. No. 3,706,723 to Chandrasekeran et al., issued Dec. 19, 1972. Hexafluoroisobutylene has been previously prepared by methods which include the reaction of hexafluoroacetone with ketene (U.S. Pat. No. 3,894,097 to N. Vanderkooi), the reaction of hexafluorothioacetone with ketene or a ketene-generating compound (U.S. Pat. No. 4,244,891 to Van Der Puy et al.), the reaction of antimony trifluorodichloride with a chlorofluoroisobutylene [R. N. Hazeldine, J. Chem. Soc., 3565 (1953)] and the dehydration of hexafluoro-2-methyl-2-propanol with phosphorus pentachloride [M. H. Kaufman et al., J. Org. Chem. 31, 3090 (1966)] or with sulfur tetrafluoride (E. E. Gilbert et al. in U.S. Pat. No. 3,656,786). These preparations and others suffer from one or more disadvantages from a commercial standpoint. For example, although the preparation involving hexafluoroacetone is a high-yield process, hexafluoroacetone represents a starting material of high cost and limited availability. The chlorofluoroisobutylene route involves several steps including a slow dehydrochlorination step, while the dehydration of the fluorinated tertiary butyl alcohol requires excessively long reaction times or expensive reagents. The reaction of hexafluorothioacetone with ketene operates in the gas phase at elevated temperature (300.degree.-800.degree. C.) and requires special reactors.
It is accordingly an object of the invention to provide a new route to hexafluoroisobutylene which utilizes cheaper and more readily accessible starting materials and which operates at milder reaction conditions in the liquid phase.
Other objects and advantages of the invention will become apparent from the following description.